The dynamic aspects of sound the amplitude and frequency changes that occur over time are crucial information-bearing elements of auditory perception and communication. This project is a comprehensive behavioral study, using normal-hearing and hearing-impaired adults, of the ability to extract information from changes in the amplitude and the short-term spectrum of sound. The proposal is divided into three related projects each of which investigates different aspects of supra-threshold dynamic processing. The general objective of the first project is to describe how we perceive changes in the level of sounds. This will be done by testing intensity increment discrimination and intensity increment matching for suprathreshold intensity increments. Especially important are the proposed experiments using hearing impaired subjects. This should provide a better understanding of the consequences of loudness recruitment on the perception of real-world sounds. The second project pursues our finding that after relatively brief exposure to supra-threshold amplitude modulation or frequency modulation there can be substantial and prolonged elevation of the threshold for detecting this feature. The general objective of the proposed research is to describe the salient properties of these aftereffects. The experiments include examination of the temporal course of recovery, frequency and level effects, binaural effects, and the effects of hearing impairment. The objective of the third project is to describe how we extract information from the (amplitude) envelope of sounds. The focus is on discrimination of the shapes of supra-threshold envelopes. The longterm objective is to develop a physiologically realistic computational model for this higher order but basic aspect of auditory perception. Overall, this project will provide information of fundamental importance for understanding the basic perceptual properties of hearing and how hearing impairment affects auditory perception. The project will help provide a bridge between auditory physiology and real-world hearing. This is essential for a full understanding of hearing and hearing loss and for the development and evaluation of strategies for alleviating the effects of hearing loss.